TOF mass spectrometry is an analytical technique for measuring the mass/charge ratio of ions by accelerating ions and measuring their time of flight to an ion detector.
In a simple form, a TOF mass spectrometer includes an ion source for generating a pulse (or burst) of ions of sample material and an ion detector for detecting ions that have travelled from the ion source to the ion detector. The ions generated by the ion source preferably have, e.g. because they have been accelerated to, a predetermined kinetic energy and so have different speeds according to their mass/charge ratio. Accordingly, as ions travel between the ion source and the ion detector, ions of different mass/charge ratios are separated by their different speeds and so are detected by the ion detector at different times, which allows their respective times of flight to be measured based on an output of the ion detector. In this way, mass spectrum data representative of the mass/charge ratio of ions of sample material can be acquired based on an output of the ion detector.
Matrix-assisted laser desorption/ionization, often referred to as “MALDI”, is an ionisation technique in which, generally, a laser is used to fire light at a (usually crystallised) mixture of sample material and light absorbing matrix so as to ionise the sample material. The sample materials used with MALDI typically include molecules such as biomolecules (e.g. proteins), large organic molecules and/or polymers. The light absorbing matrix is generally used to protect such molecules from being damaged or destroyed by light from the laser. The resulting ions, which typically have masses of several thousand Daltons, are then accelerated to high kinetic energies, typically around 20 keV. Generally, an ion source configured to generate ions by MALDI is referred to as a “MALDI ion source”. A MALDI ion source typically includes a laser for ionising sample material by firing light at a mixture of the sample material and light absorbing matrix.
MALDI is usually combined with time of flight mass spectrometry to provide “MALDI TOF” mass spectrometry in which, generally, a pulse of ions is generated by MALDI and the time of flight of the ions is then measured over distances typically of around 1-2 metres so that the mass/charge ratio of the ions can be determined.
Measuring the time of flight of ions in modern TOF mass spectrometers, e.g. MALDI TOF mass spectrometers, typically requires a diverse range of high speed digital and analogue electronics. For example, high speed timing electronics may be used in order to accurately synchronise various high-voltage electrical pulses with the firing of a laser and the acquisition of an ion signal. Also, kV/·s slew-rate high voltage electrical pulses may be used to accelerate, gate and steer ionised molecules generated by the laser. Finally, high speed multi-bit analogue to digital converters may be used to record the output from an ion detector so that the time of flight of the ions, and therefore the mass/charge ratio of the ions, can be determined. Such high speed digital and analogue electronics are typically run for each acquisition cycle of the TOF mass spectrometer.
Until recently, TOF mass spectrometers, e.g. MALDI TOF mass spectrometers, have used gas lasers having a repetition rate (rate at which it can fire pulses of light) of up to a few tens of Hz. More recent TOF mass spectrometers have used solid-state lasers capable of much higher repetition rates, e.g. 1 kHz or more.
The present inventors have found that high repetition rates of solid state lasers, combined with increasing clock speeds of digital electronics, has introduced new problems in the design of TOF mass spectrometers, particularly MALDI TOF mass spectrometers. These design problems include:                how to generate multiple high-precision delays (e.g. with microsecond durations and sub-nanosecond resolution);        how to stabilise power supplies to the electronics without radiating a lot of narrow-band electrical noise, especially for high-voltage pulses; and        how to reduce the manifestation of noise in mass spectrum data produced by such MALDI TOF mass spectrometers.        
The present invention has been devised in light of the above considerations.